Immunoproteasome functions explained by divergence in cleavage specificity and regulation

Area of Science:

• Biochemistry
• Immunology
• Molecular Biology

Background:

• The immunoproteasome (iP) is implicated in immune functions like antigen presentation and cytokine modulation.
• The iP is a therapeutic target for autoimmune diseases and cancer.
• Functional differences between the iP and constitutive proteasome (cP) remain largely undefined.

Purpose of the Study:

• To elucidate the functional divergence between the iP and cP.
• To investigate the substrate specificities of the iP and cP.
• To explore the therapeutic implications of iP-specific characteristics.

Main Methods:

• Utilized a global peptide library for screening proteasome substrate specificities.
• Developed and employed isoform-selective substrates.
• Conducted cellular profiling to assess proteasome regulation and function.

Main Results:

• Identified overlapping yet distinct substrate specificities for iP and cP.
• Demonstrated that iP specificity influences MHC I epitope quantity but not preferential antigen presentation.
• Revealed that iP specificity likely evolved through genetic drift from the cP.
• Showcased selective recovery from inhibition in immune cells due to regulatory divergence of the iP.

Conclusions:

• The functional divergence of the immunoproteasome is linked to its distinct substrate specificity and regulatory mechanisms.
• Understanding these differences is crucial for developing targeted immunoproteasome therapeutics.
• The findings provide a basis for selective drug development against the immunoproteasome for immune-related conditions.